1. Field of the Invention
The present invention relates to apparatus for still picture video telephone and methods for transmitting and displaying still picture image for use therein.
2. Description of the Prior Art
There are demands for a video telephone system capable of simultaneously transmitting audio and video information through a telecommunication line. By the use of the telecommunication line today, however, it is difficult to continuously transmit and receive a moving picture because it requires huge amounts of data. Hence, at present, a still picture video telephone system which transmits a still picture image during a telephone call is being put into practical use.
The still picture video telephone is a system capable, in the course of a telephone conversation with an ordinary voice signal, of temporarily stopping the conversation and transmitting, in the meantime, a desired still picture, such as the face of the speaker, photo, picture, and drawing relative to the contents of the conversation.
According to such a still picture video telephone system, it is made possible to transmit and receive a picture image through a telephone line, which in the past was impossible, and the processed data quantity is not so large because only a single still picture is transmitted at a time, and therefore, there has been an advantage that the video telephone system can be easily put into practical use.
Such a video telephone system capable of transmitting a still picture is disclosed, for example, in "Overseas Telecommunications Technology", October 1986. FIG. 1 is a circuit configuration diagram of the simplified still picture video telephone apparatus disclosed therein. Referring to the drawing, reference numeral 1 denotes a hand set, 2 denotes a microphone, 3 denotes a voice input/output circuit, 4 denotes an analog circuit, 5 denotes a matrix switch, 6 denotes a telephone interface circuit, 7 denotes a telephone line connection terminal, 8 denotes a speaker, 9 denotes a key pad, 10 denotes an input/output port, 11 denotes a CPU, 12 denotes a program memory, 13 denotes a modulator/demodulator circuit, 14 denotes a television camera, 15 denotes an image controller, 16 denotes a picture memory, and 17 denotes a display.
Operation for transmitting audio and video signals in that prior art video telephone apparatus will be described with reference to FIG. 2. Speech by voice is delivered from the hand set 1 or microphone 2 through the voice input/output circuit 3, the analog circuit 4, the matrix switch 5, and the telephone interface circuit 6 to the telephone line connection terminal 7. The audio signal from the person on the other end of the line is passed through the above signal path in the opposite direction and reproduced by the hand set 1 or speaker 8.
When transmitting a picture image signal in this case, the transmitter side sends a header including an ID code such as data on communicating capability to the receiver side for confirming that the set on the receiver side is a video telephone apparatus capable of communicating picture data in the same data format. After confirming that the other party has the same capability upon receipt of a header therefrom, the transmission of the picture data is carried out.
More particularly, with reference to FIG. 1, when an instruction for transmitting a picture image is issued with the use of the key pad 9, the CPU 11 detects this through the input/output port 10, and delivers a header in accordance with a program previously stored in the program memory 12 to the modulator/demodulator circuit 13. Therein, the header is converted into an analog signal and this signal is then transmitted through the matrix switch 5 from the telephone line connection terminal 7. The header from the other end is passed through the same path in the opposite direction and subjected to confirmation by the CPU 11 as to its code or the like.
In the meantime, picture images picked up by the television camera 14 are quantized in the image controller 15 and stored in the picture memory 16, and then, led out to the display 17 to be displayed thereon in succession, and the stored picture data are read out from the picture memory 16 under the instruction of the CPU 11 and delivered to the telephone line connection terminal 7. Incidentally, the picture data has a header added thereto indicating the data length or the like.
When the header from the other end of the line is received, it is acknowledged that reception of picture data will be started, and the matrix switch 5, based on a received carrier signal, switches, from the analog circuit 4 to the modulator/demodulator circuit 13, the delivering path of the incoming signal from the telephone interface circuit 6. After the received signal is demodulated in the modulator/demodulator circuit 13, the CPU 11 sends back a header or stores the data in the picture memory 16. Thereafter, the image controller 15 leads out the picture data prepared in its own system and the picture data received from the system on the other end from the picture memory 16 in succession to be displayed on the display 17. Also to the front of ordinary picture data is attached a simple header including an indication that picture data will follow.
When the transmission and reception of image data have been finished and there is no more carrier signal from the modulator/demodulator circuit 13, the matrix switch 5 connects the telephone interface circuit 6 with the analog circuit 4 and thereby resumes the voice communication.
In the case where the answerback from the receiver side is to be omitted, the information that it can be omitted is put in the header and picture data is transmitted in succession to the header. Even in this case, the receiver side, upon receipt of the header, prepares the arrangement for receiving the picture data in the same manner as described above.
Incidentally, the picture memory 16 of the prior art is composed of a camera-taken picture memory portion which stores picture information input from its own television camera 14, rewriting it at intervals of a predetermined period (e.g., 1/30 second), and an incoming picture memory portion for storing picture information obtained by demodulating still picture information received from the system on the other end of the line during the telephone call, and the memory portions of the picture memory 16 each have storage capacity for one page of picture information.
Now, the picture image display performed by the prior art video telephone apparatus at the time of signal reception will be described.
In the prior art video telephone apparatus, the transmitted and received picture image has only one resolution. Hence, as shown in FIG. 3, the video telephone apparatus reads out the image data stored in the region for storing the received image data in the picture memory 16 and displays this data on the display 17. In the event that it has received new picture data under that condition, it writes the received picture data in the same region of the picture memory 16. More particularly, as shown in FIG. 4, the received picture data is overwritten in the region for storing the received picture data in the picture memory 16.
The display on the display 17 in this instance is, as shown in FIG. 5, sequentially rewritten from the top of the picture plane. More particularly, FIG. 5(A) indicates the state on the display 17 before reception of new picture data, FIG. 5(B) indicates the state in the course of the reception, and FIG. 5(C) indicates the state when the reception has been finished.
Since the storage region of the camera-taken picture memory portion and the incoming picture memory portion in the picture memory of the prior art still picture video telephone apparatus each just have capacity for one page picture information as described above, there has been a problem that it is impossible to have picture information stored prior to transmission of a picture image.
Further, in the case where it becomes necessary to talk over a plurality of pages of picture information during a telephone call, since the picture memory has been renewed, there has been such a problem that a picture image which was earlier transmitted must be requested to be transmitted again, and therefore, the conversation has to be stopped on each of such occasions.
Furthermore, in the prior art still picture transmission technique, the reading out of the picture data from the picture memory 16 has only been possible to be performed in the unit of a predetermined frame.
Hence, a demand for such a performance of the system to have only a specific portion extracted from the unit picture data, excluding unnecessary data therefrom, and to transmit only the necessary data, thereby saving time for transmission, has not been met.
Further, in the case where the display picture plane of the system on the receiver side is smaller than the picture plane on the transmitter side, transmission in the prior art of all of the unit picture data corresponding to the whole display plane on the transmitter side involves a large loss of transmission cost and time.
Furthermore, when the resolution of the newly received picture data is different from the resolution of the previously received picture data, the prior art video telephone apparatus is unable to make a normal display. For example, if the resolution of the earlier received picture data was 160.times.100 as shown in FIG. 6(B) and the resolution of the newly received picture data is 96.times.100 as shown in FIG. 6(A), then the data array in the picture memory 16 becomes as shown in FIG. 6(B). Hence, it follows that there are picture data of two kinds of resolutions mixed in the picture memory 16. Therefore, in such a case, it has been impossible to decide with which resolution to make the display and it has been difficult to make a normal display on the display 17. Further, there has been such a problem that, when the data is read out from the picture memory 16 with either of the resolutions and thereby displayed on the display 17, the picture image with one of the resolutions is greatly disturbed and an obscure display is made.
Besides, there has been a problem in the prior art still picture video telephone transmission system that, when picture data has been transmitted from a still picture video telephone apparatus having a different aspect ratio of vertical height to horizontal width of the picture plane, it cannot be displayed.